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Top One Tech discuses types of capacitive touchscreens

Capacitive touch screen is a kind of display utilizing the electrical properties of the human body as an input way. When a finger or input device like a stylus comes in contact with the display it detects when and where on the display the touches are. Capacitive screens are mainly divided into two types: surface capacitive screens and projected capacitive screens, and projected capacitive screen technology is divided into self-capacitance and interactive capacitance.

Surface Capacitive Screens
Surface capacitive touch screens sense touch behavior on the screen surface through electric field induction. Its panel is evenly coated with an ITO layer. Each of the four corners of the panel has an outlet wire connected to the controller. During operation, a uniform electric field is generated on the surface of the touch screen. When a grounded object touches the screen surface, the electrodes can sense the change in charge on the screen surface and identify the coordinates of the touch point.

Surface capacitive touch screens have long service life and high light transmittance, but have low resolution and do not support multi-touch. They are currently mainly used in large-size outdoor touch screens, such as public information platforms (POI), public service (sales) platforms (POS), etc.

Projected Capacitive Screen
Projected capacitive touch screens utilize electrostatic field lines emitted by touch screen electrodes for sensing. Projected capacitive sensing technology can be divided into two types: self-capacitance and interactive capacitance.

Self-capacitance is also called absolute capacitance. It uses the sensed object as the other plate of the capacitance. The object induces charge between the sensing electrode and the sensed electrode, and the touch position is identified by detecting changes in the coupling capacitance. But if it is a single touch, through capacitance changes, there is only one set of coordinates identified in the X-axis and Y-axis directions, and the combined coordinates are also unique. If there are two points touched on the touch screen and the two points are not in the same X direction or the same Y direction, and there are two coordinate projections in the X and Y directions respectively, four coordinates will be combined. Obviously, only two coordinates are real, and the other two are commonly known as “ghost points”. Therefore, self-capacitive screens cannot achieve real multi-touch.

Interactive capacitance is also called crossing capacitance. It is the capacitance generated by the coupling of adjacent electrodes. When the sensed object is close to the electric field line from one electrode to another electrode, the change in interactive capacitance will be sensed. When the horizontal electrodes send out stimulation signals in sequence, all the vertical electrodes receive the signals at the same time. In this way, the capacitance value of the intersection of all horizontal and vertical electrodes can be obtained, that is the capacitance of the entire two-dimensional plane of the touch screen. When human fingers approach, the local capacitance will decrease. Based on the two-dimensional capacitance data change of the touch screen, the coordinates of each touch point can be calculated. Therefore, even if there are multiple touch points on the screen, each touch point’s real coordinates can be calculated.

In both types of projected capacitive sensors, the sensing capacitance can be designed in a given way that the touch of a finger is detected at any given time. The touch is not limited to one finger, but can also be multiple fingers. Since 2007, with the great success of Apple’s iPhone and iPad series products, projected capacitive screens have begun to develop rapidly, quickly replacing resistive touch screens and becoming the mainstream touch technology in the market.

Advantages of Projected Capacitive Screens
The advantages of projected capacitive screens are as follows:
1. High definition: Projected capacitive screens have high-resolution and high-density pixels, enabling clearer and more detailed images and text.
2. Multi-touch: The projected capacitive screen supports multi-touch, allowing multiple people to operate at the same time, improving the user’s interactive experience.
3. Fast response speed: The projected capacitive screen has a very fast response speed and can achieve real-time response, improving the user’s operating efficiency.
4. Space efficiency: Projected capacitive screens can be directly projected on a flat surface or wall, without the need for additional displays.
5. Good display effect: The projected capacitive screen has a very good display effect, with bright colors, high brightness and strong contrast, which can present more realistic and vivid images and videos.
6. Easy to maintain: Projected capacitive screens have no mechanical parts, and are not easily damaged, enabling low maintenance costs and long service life.

Projected capacitive screens have the characteristics of high sensitivity, high precision, fast response, and support multi-touch. They are widely used in electronic products such as smartphones, tablets, TVs, and car navigation systems.
Saturday, October 7, 2023

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